Diversity and function of arthropod endosymbiont toxins

• Published in: Trends in microbiology (Regular ed.) Vol. 30; no. 2; pp. 185 - 198
• Main Authors: Massey, Jonathan H., Newton, Irene L.G.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.02.2022; Elsevier Science Ltd
• Subjects: Animals; Arthropods; Bacteria; Cytoplasmic incompatibility; Endosymbionts; Enzymatic activity; Homology; Incompatibility; Male; Molecular modelling; Nuclease; Parthenogenesis; Pathogens; Phenotypes; Phylogeny; Proteins; Rickettsia; Symbiosis; Toxins; Wolbachia - genetics
• ISSN: 0966-842X; 1878-4380
• DOI: 10.1016/j.tim.2021.06.008

Bacterial endosymbionts induce dramatic phenotypes in their arthropod hosts, including cytoplasmic incompatibility, feminization, parthenogenesis, male killing, parasitoid defense, and pathogen blocking. The molecular mechanisms underlying these effects remain largely unknown but recent evidence suggests that protein toxins secreted by the endosymbionts play a role. Here, we describe the diversity and function of endosymbiont proteins with homology to known bacterial toxins. We focus on maternally transmitted endosymbionts belonging to the Wolbachia, Rickettsia, Arsenophonus, Hamiltonella, Spiroplasma, and Cardinium genera because of their ability to induce the above phenotypes. We identify at least 16 distinct toxin families with diverse enzymatic activities, including AMPylases, nucleases, proteases, and glycosyltransferases. Notably, several annotated toxins contain domains with homology to eukaryotic proteins, suggesting that arthropod endosymbionts mimic host biochemistry to manipulate host physiology, similar to bacterial pathogens. Arthropod endosymbiont genomes contain multiple proteins with homology to bacterial protein toxins.Among Wolbachia, Rickettsia, Arsenophonus, Hamiltonella, Spiroplasma, and Cardinium genera, we identify at least 16 distinct toxin families.Several toxins contain multiple domains, share homology with eukaryotic proteins, and are encoded by bacteriophage genomes.Toxins known to induce male killing, cytoplasmic incompatibility, or parasitoid defense target host DNA or RNA.Arthropod endosymbionts might induce many of their host phenotypes via toxin secretion.